In these kinds of vehicle control apparatus, validity of each wheel speed, which is used to calculate a vehicle speed, should be assured for properly performing a vehicle control based on the vehicle speed. Especially, during low speed running, an output of a wheel speed sensor could be below a speed which is detectable by the wheel speed sensor, leading to unreliable detection values. Therefore, a minimum calculable value of the wheel speed, i.e. a valid wheel speed, should be set to a threshold value to accurately determine the validity of the wheel speed.
In JP H7-257352A, a vehicle control unit is disclosed. A minimum calculable value of a wheel speed or an allowable speed, at which the vehicle control is allowed to be conducted, whichever is greater, is set to a selected value. Then, the vehicle control unit compares the selected value and the vehicle speed to determine whether or not the vehicle control should be conducted.
However, in the vehicle control unit disclosed in JP H7-257352A, the wheel speed, which is first calculated after the vehicle starts running, is set as the minimum calculable value. In such a case, the minimum calculable value may not be accurately calculated in the following situations due to influences caused therein. For example, in case that the vehicle is accelerated rapidly from a standstill, in case that noise occurs in at output of the wheel speed sensor, or in case that filtering is performed in the wheel speed calculation, the minimum calculable value may not be accurately calculated. This drawback is observed prominently when constant speed control is conducted at a low speed as disclosed in JP 2004-90679A.
The present invention is made in view of the drawbacks described above and provides a vehicle control apparatus which accurately calculates a minimum calculable value of a wheel speed, i.e. a valid wheel speed, to prevent control malfunction even in the above-described situations.